As this kind of electric motor control apparatus, there is known one in which control is performed by a torque command signal generated based on a velocity signal or a position signal of an electric motor so that the torque of the electric motor coincides with the torque command signal, and a load machine connected to the electric motor through a torque transmission mechanism is driven. However, there has been a problem that because of low rigidity of the torque transmission mechanism to couple the electric motor and the load machine, it is difficult to simultaneously realize an improvement in disturbance suppression force and vibration of the load machine.
Then, a conventional electric motor control apparatus is constructed such that a signal obtained by multiplying an acceleration signal of a load machine by a proportional characteristics is subtracted from a torque command signal generated based on a velocity signal and a position signal of an electric motor, and the vibration of the load machine included in the acceleration signal of the load machine is reflected in the torque command signal so that the vibration of the load machine is suppressed (see, for example, patent document 1).
Alternatively, a structure is made such that a vibration suppression circuit is added which inputs an acceleration signal of a load machine and corrects a torque command signal outputted by a position control circuit, an electric motor, the load machine, the position control circuit and the vibration suppression circuit are represented by a model of a state equation, and gains of the position control circuit and the vibration suppression circuit are determined so as to minimize an evaluation function including terms in which a position deviation, acceleration of the load machine and operation energy to be given to the motor are taken into consideration and state variables of the state equation, so that responsibility for the command is improved without vibrating the load machine (see, for example, patent document 2).
Patent document 1: JP-A-6-91482
Patent document 2: JP-A-5-303427